Automatic defrosting system for refrigeration machines



M. S. SUTTON Dec. 15, 1953 AUTOMATIC DEFROSTING SYSTEM FOR REFRIGERATION MACHINES Filed Feb. 6, 1951 THY? / EVAPURATOR CONDENSER (0MPRE550R l RECEIVER H ATTORNEYS.

Patented Dec. 15, 1953 AUTIOM'ATICIDEFROSTING SYSTEM FoRI REFRIGERATION MACHINES 7 Claims.

This invention relates: to a refrigeration machine and it relates more particularly to an new and improved: defrosting; system for controlling? the operation of the-refrigeration unit..

a: refrigeration machine: oi the type adapted: to make most. effective. use of the concepts of this inventiom air is causeda to travel over a cooling? surface, such: as the coils of. an. evaporatorthrouglrwhielr refrigerant is being circulated. As the air is re'ducedi'in: temperature for cooling: the space to: be: refrigerated, some; moisture in the air condenses almost immediately con-- goals as a: frozen-substance or frost onto'thesu-r faces oi the: cooling element. The frost layer operatesiasea barrierto heat; transfer and as the thickness of the: layer oiiirost. increases;.- the chi-- ciency of thesretrigeration unit. is markedly-re;- duced. As a result, it: is expedient periodical 1y to remoivc the:ctrost; layer from the surfaces of. thecooling element on soils: The: frequencyof, defrosting. dependsgreatly upon: the: amount of" outsideair admittedinto the; machine and the; humidity! conditions: existing;

Defrosting has usually' been carried out in: the; past; stoppingi thecirculation of refrigerant; through the: cooling; element or substituting hot gases or other medium for the reirigenant; passing? through the coils; to increase: theternperature'soifthet cooling; elementtoith'e point; where;

the frost melts; so; as; to. permit; removal from the: 7

thesubstantially simultaneous; circulation. of. air" amt-"refrigerant following melting. of; the; frost;

during, the first; stage of the def rosting: cycle; permitsrthei-airr toa 'picki up; droplets; of, waterv which might remainom the: sunfaces.v of the; cooleing;element and: carr them 17.02 the space 1703 1385- co'olect.. Irr the; second place, suchsystems: per mitsthe circulationoi 'ai-r oven the coilsand intothe-spac'eTto be. refrigerated before the soils havehad anopportunity to. reach coolin "temperatur-e.-

Asa result; the: air circulated dun gan; initial portion of 'the'cycle is heated instead of bein-g 2.1 cooled and correspondingly reduces thetemperature within therefrigerated space;

More important: systems of the type described have beeninca'pabl'e of sufficient flexibility which takes into consideration differences that mightexist in the thickness of the-layer condensedand frosted on the surfaces or the coolingelement; When operating primarily on a time cycle; instances will be encountered where the frosted layer is-so thick as to he only partially removed, if at all, duringthe interval provided formelt' ing. Onother occasi'ons',--the layer off'rostmay be so thin as topermit complete removal in a fraction of" the time allowed; either even-t eflicient operationis not" achieved.

It is an. object of'this invention to" producea new and improved refrigeration machine characterized by an efiic'ient and efiecti'ye defrosting system and it is a related object toprovide a new and improved defrosting system for a refrigeration machineoi the type described.

Another object is to produce a refrigeration machine having a defrosting: system which provides for substantially complete elimination of frost from the surfaces of the cooling element before steps are taken for return to normal refrigerating conditions which provides for. delay in thecirculation of air" until the cooling" el'e-= ments' have been returned" to conditions for cooling, and which provides for commencing the recirculation of air over the cooling elements automatically in response to the condition of the cooling element, and it is. a related object tocause the succession of, steps, automatically take place in response to conditions existing;

A further object is to produce a. defrosting, system ina refrigeration machine of, the," type described which is free of the objectionable features existing. in earlier systems and'wh'ich is composed of relatively few simple parts which are" readily" assembled into a compact structure which is capable of continuous and economical operation.

These and other" obj cots and advantages of this il iventien will hereinafter" appear and for cur: poses-cf illustration, but not of limitation; an

embodimentof -this inventionis shown in the accompanying drawing" in -wh-i-cl1 Figure-1 is-a schematicdiagram of the electricalsystem and controlsembodied in the present invention; and

Figure 2 is aschematic layout of a refrigez-ation system: embody-ing 'features of this invention;

This invention is a further improvement" over asystemdescribed and claimed in the J ones Pat-= aeeaso 3 ent No. 2,509,099, wherein the return of the cooling coils to refrigerating conditions independent of the return to operation of the means for circulating the air over the cooling coils is thermostatically controlled from the surfaces of the cooling coils. When the frost has been eliminated from the surfaces of the cooling coils so that a rise in temperature is enabled, the thermostat becomes effective at a predetermined temperature level to cause cut-off of the hot gases passing through the coils and re-entrance of cooling liquids. The start of air circulation to complete reinitiation of the refrigeration cycle is time controlled from the start of the defrost cycle as the base, such as about three quarters of an hour from the time the defrost cycle was initiated. The defrost cycle itself is time controlled for operation at certain periods, such as for defrosting early in the morning and again late in the afternoon in commercial dispensing and display units.

It has been found that there are certain inefficiencies which still exist on occasion in the Jones system. For example, when the build-up of frost on the outer wall of the cooling elements or coils is of such magnitude that defrosting cannot be completed before time for air circulation, it will be apparent that the coils will still carry a large amount of water on the surface in droplets which may become entrained in the air system and, furthermore, air may be caused to pass over the coils before they have been cooled down to the desired temperature and complete removal of frost will not have been achieved. On the other hand, if very little frost has collected on the surfaces of the cooling element, removal thereof and reinitiation of the circulation of refrigerant through the cooling element will occur very shortly and the coils may be reduced to a sufficiently low temperature long before the time for air circulation with the result that the temperature in the space to be refrigerated is permitted to rise higher and to remain uncooled for a longer period of time than would be necessary.

Therefore, a still further object of this invention is to produce a refrigeration machine which periodically and automatically provides for defrosting the refrigeration unit completely to remove any and all frost accumulation in an endcient and effective manner.

Another object is to provide in combination with a refrigeration system having means for defrosting the evaporator thereof by circulating heating medium therethrough, a system for periodically admitting the heating medium to the evaporator for purposes of melting the frost to terminate the flow of heating medium as soon as the frost has been removed from the surfaces of the evaporator and for initiating the circulation of air to complete the refrigeration cycle when the evaporator is reduced in temperature to cooling conditions.

In accordance with the present invention these conditions are taken into account and greater flexibility provided to the operation of the refrigeration machine by use of means not only for initiating the cut-off of the hot gases and recirculation of the refrigerant responsive to the temperature at the surface of the coils, but also to initiate recirculation of air to complete return to refrigerating conditions responsive to thermostatic conditions existing at the surface of the coil. In this way, assurance is had to the initiation of the cooling step when all of the frost has been removed and air circulated over the coils and into the space to be refrigerated as soon as the coils reach low enough temperature. Such conditions also provide for congealing any droplets of water that might inadvertently remain on the surface of the evaporator coils before air circulation so that conditions for entrainment will not be available.

The inventive concepts are illustrated in a refrigeration system, shown in Figure 2, comprising a compressor l0 adapted to be operated by a suitable power source, such as an electric motor or internal combustion engine (not shown). The compressor is connected on its high pressure side by tubing 1 I to one end of a condenser [2 whereby hot gases are delivered under high pressure to the condenser for conversion into liquid refrigerant which flows from the outlet end of the condenser through passage [3 to a liquid receiver 14.

Another passage [5 communicates the receiver M with the inlet end of an evaporator l6 formed of a plurality of coils. Flow of refrigerant from the receiver to the evaporator is controlled by an expansion valve ll. Valves suitable for such purposes are well known in the art and need not be described herein great detail. Suffice it to say that a preferred valve has a pressure responsive operator, such as a bellows or the like, located within the valve body which is made to close the valve in response to increased pressure and opens the valve to permit fluid flow therethrough upon decrease of pressure operating from the direction of the evaporator on the valve body.

The low pressure side of the compressor [0 4 connects to the outlet end of the evaporator 16 A container, such as a drip pan 2 i is positioned beneath the evaporator to collect material which falls therefrom during defrosting and heaters 22, such as electrical resistance heating elements, are located in operative relation with the pan to reduce frozen particles therein to fluid consistency for permitting drainage therefrom and complete removal. An air circulating fan 23 is located to one side of the evaporator for the purpose of.

directing an air stream across and through the coils of the evaporator whereby the air is reduced in temperature during the cooling cycle and advanced for cooling the space to be refrigerated.

as will hereinafter be described. a

The sequence of operations of these refrigeration elements are adapted to be automatically controlled. As shown in Figure l, the controlsystem comprises lead wires 30 and 3| which conneat to a suitable electrical power source. The numeral 32 indicates a single pole, single throw switch having switch arm 33 operatively connected to a timing device adjusted periodically to make contact with point 34 for initiating the automatic defrosting cycle, which will hereinafter be pointed out. Numeral 35 indicates a standard relay having a switch arm 36 shiftable upon actuation by a relay coil and plunger assembly 31 between contact point 38 leading to fan escapee.

23 and contact point 39 leading to. the heater 22 and the solenoid 40 which operates the. valve member 20.

Numeral 41 is a thermostat having one switch arm 42 adapted to make or break with contact point 43 responsive to the temperature recorded by thermostat bulb id positioned in thermal re.- sponsive position to record temperatures existing at the surface of the coil and positioned substantially in surface contact therewith. A second switch arm 45;. in thermostat 4.! is shiftable tov make or break with contact point 16 in re-. sponse. to. rise of the temperature thermostat bulb to a difierent temperature level, as will herein after be pointed out.

When the unit described is operating in its normal refrigeration cycle, that is when high pressure gases are delivered from. the. compressor [.0 to. the, condenser i2 for liquefying and admitted into the receiver i l and from the receiver M to the. evaporator it for cooling the coils and then returned to the compressor for completing the. cycle, valve 20 is closed to prevent passage of hot gases from the high pressure side of the com-. pressor. Valve I7 is open topermit refrigerant to flow from the receiver to the inlet end of the evaporator.

During such normal operation as a refrigeration unit, switch arm 36. is in the raised position to contact. point. 33.. Switch arm d2 of the thermostat is in contact with point 43. so that fan 23.. will be. in the circuit and operated to direct a stream of air across and through the coils of the. evaporator l6. During such operation, sole-,

noid all will be deenergized so as to cause valve 29.. to. remain closed and prevent travel of hot gases from the condenser and, compressor to the evaporator. When the time, which is predetermined by clock mechanism or the like, arrives for initiating the defrosting cycle, switch arm 33. is thrown in the direction to make contact with point 3.4. Such movement of switch arm 33 is. only momentary to close switch 32 and. energize relay coil 31 which retracts plunger 3.7 and rocks Switch arm 36. in the direction to break with contact point 38. and make with contact point 39-. Thus, fan 23 is disconnected from the power source and operation thereof ceases. Electrical current flows from contact point 3% to switch arm d5 normally in position to make with contact. point 46. Thus current flows to solenoid 4!] for opening valve 20 to permit hot gases at high pressure to flow from the high pressure sideof'the compressor and the condenser to the evaporator coils for increasing the temperaturethereof and connection is also established with heater 2.2 to increase the temperature thereof for melting any ice or other frozen material which might fall into pan 2!. Making of the switch comprising switch arm 5 to contact point 46 also enables current to flow to relay coil 31 so as to keep it energized notwithstanding the return of switch 3-2 to normal conditions so that solenoid 40 and heater 22 will remain energized through the initial stages of the defrosting cycle.

Responsive to the-introduction of high pressure hot gases into an intermediate portion of the evaporator t5, the bellows system or other pressure responsive actuator in the body ofvalve IT automatically becomes operative to close the valve and stop flow of refrigerant from the receiver to the condenser. The heat introduced into the evaporator by the hot gases causes rapid melting. of the frost deposited thereon and providesfor arise in temperature at the surface of the coils when substantially all of the frost has been removed.

Th described conditions for defrosting is adapted to continue while the frost is being removed from the surface of the evaporator and drops as water or ice into the heated pan 2i where the heater 22 can quickly reduce any solids. to fluid consistency. Until substantially all of the frost is removed it will be obvious. that the temperatures existing on the surface of the evaporator will not rise much above 32 F The thermostat may be setto be responsive to a rise in temperature of the evaporator coils to. a predetermined highertemperature level, such as 45 F., as register-ed by the bulb Mi. When such temperature is reached and the thermostat tripped, switch arm 45- breaks from contact point 4'6, at the same time switch arm 22 breaks from contact point "43. This disconnects heater 22 for deenergiaationthereof and it also deenerg-izes solenoid 4E? whereby the plunger returns. to.- starting position and closes hot gas valve 2-8 and it: also deenergizes relay coil 37 so that plunger 3? returns and causes switch arm to break with contact point 35 and make with contact point 38.

As a result, communication is cut off between the high pressure side of the compressor and the evaporator with the result that the expansion valve Ell automatically opens to reestablish the circulation of refrigerant between the receiver it and evaporator If} whereby the coils of the evaporator are subjected to cooling conditions. The fan still remains inactive because of the break between switch arm 3?. and the contact point 43 in the thermostat.

When the normal now of refrigerant through: the evaporator causes reduction in temperature on the surfaces thereof to a point which freezes drop-lets or other moisture that might have remained thereon and to present a surface for cooling the air, the thermostat @i is adapted to be tripped again and reestablish contact between switch arm t2 and contact point 53 t insert the fan 23 in the electrical circuit and set it in operation. For example, the thermostat may beset to be tripped when the bulb l irecords a temperature of about 15 F. on the surface of the coils. Thus the unit automatically passes through a defrost cycle and returns the elements to normal operative conditions for refrigeration.

During the cycle for defrosting, it will be apparent that the compressor and condenser are in direct communication sc that the hot gases taken from a point between these two units will be bled from each for introduction into the evaporatorat a point intermediate the inlet and outlet. Introduction at this point enables the hot gases to compensate and overcome the cooling effect of the refrigerant. Such gases are returned to the compressor from the outlet of the evaporator to provide an endless cycle.

Heat for defrostingin this manner is obtained chiefly as the result of the work of the compressor, especially if activation thereof is by anelectric motor or the like. In the event that'the power for the compressor is derived from an in-- ternal combustion engine, the high heat occasioned by its operation may be utilized to an extent as a source of heat for the defrosting operation.

It will be evident from the description that thecompressor remains in operation throughout the defrosting cycle and is also in operation through the refrigeration cycle, except for those periods of time when the space to be refrigerated is 7 flown to' desired temperature. During the defrosting cycle, expansion valve I! is automatically closed to stop circulation of refrigerant from the condenser to the receiver and from the receiver to the evaporator, thereby to inactivate the cooling members until the frost is completely removed from the surface of the evaporator and the thermostat fl tripped for the first time. When defrosting has been completed and pressure is reduced in the evaporator because of the cut-off of hot gases, the conditions existing cause expansion valve l! automatically to open so that liquid refrigerant can reenter the evaporator to continue the cooling cycle.

It will be understood that the thermostat may be set for operation at other temperatures than those which have been described. The temperature at which the thermostat is tripped for the first time to stop the flow of hot high pressure gases and cut off the heater 22 for return to the cooling cycle should be above 32 F. and preferably above 37" F. For economical operation the thermostat should be set to be tripped at a temperature below 50 F., but higher temperatures may be used. The temperature at which the thermostat should be set to return the fan to operation after the cooling coils have been reduced in temperature should be below 32 F. and preferably below 27 F. For most economical operation, it should not be less than F. but

lower temperature response may be used. A rise of 5 F. or more during defrost indicates frost elimination from the surfaces of the evaporator coils and at a drop of temperature to below 27 F. there remains little possibility that droplets of water or the like will still remain on the surface of the evaporator for objectionable entrainment into the air stream.

It will be understood that other means for providing an air stream may be employed, but when air circulation is forced, actuation thereof over the evaporator coils should be controlled to eliminate contact with the evaporator during the time that circulation of the refrigerant is stopped and until the coils are once more returned to proper cooling temperature.

It will be apparent from the description that I have provided a system wherein the entire defrosting operation, once it has been started, proceeds automatically under controls operating in accordance with the conditions existing during the defrost cycle without embodying inflexibility and rigidity of the type which is introduced by reliance on a time cycle. When the frost is removed, no matter how little time or how much time is required, the cooling cycle begin anew. When the coils are again down to cooling temperature, even though that may take five minutes or two hours after the defrost cycle has been initiated, air circulation is automatically commenced. Thus, most eihcient and effective use is made of time and equipment and the contents in the space to be refrigerated is subjected to less possibility of spoilage or the like.

The concepts described and claimed herein are adapted for use in a refrigeration machine having a closed cabinet through which the cooled air is circulated. Instead of a closed food containing cabinet the system may be used in an open type cabinet wherein the cooled air is introduced into the well or the like in which the packages to be refrigerated are stored, or it may be adapted for use with a combination of such units, such as an open type cabinet having a closed superstructure with compartments or the like in which packages to be maintained under refrigerating conditions are stored.

It will be understood that numerous changes may be made in the details of construction, arrangement and operation without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. In a refrigeration machine having an evaporator through which refrigerant is circulated to reduce the evaporator to cooling temperature and means for causing a stream of air to pass over the surfaces of the evaporator and into the space to be refrigerated, means intermittently operative responsive to time control for introducing heated fluid medium at high pressure into the evaporator to increase the temperature thereof and substantially simultaneously for inactivating the means for causing air flow, a thermostatically controlled element responsive to the temperature on the surfaces of the evaporator to stop circulation of the heated medium through the evaporator whereby refrigerant is allowed to continue therethrough when the temperature on the surfaces of the evaporator rise above freezing, and means responsive to the thermostatically controlled element for reactivating the means for causing air circulation over the evaporator when the temperature thereof falls to below freezing subsequent to circulation of refrigerant therethrough.

2. In a refrigeration machine having an evaporator through which refrigerant is circulated to reduce the temperature thereof and means for circulating air over the evaporator and into the space to be refrigerated, time controlled means set to initiate the defrost cycle to cause hot fluid to flow through the evaporator and increasin the temperature thereof and substantially simultaneously inactivating the means for circulating air thereover, a thermostatically controlled element responsive to the temperature at the surface of the evaporator to inactivate the means for circulating heated medium through the evaporator without reactivating the air circulating means when the surface of the evaporator rises to a temperature above 37 F., and means for initiating operation of said air circulating means responsive to actuation of said thermostatically controlled element when the temperature at the surface of the evaporator falls to below 27 F.

3. in a refrigeration machine having an evaporator through which refrigerant is normally adapted to flow for reducing the temperature at the surfaces thereof and means for circulating air in surface contact with the evaporator and into the space to be cooled, a passage connecting the evaporator with a source of low pressure heated fluid for introducing such heated medium into the evaporator during the defrost cycle, an electrically operated valve member for controlling the flow of fluid through said passage, means set for periodic operation for adjusting said electrically controlled valve to cause flow of heated fluid from the source into the evaporator and substantially simultaneously to inactivate the air circulating means, a thermostat responsive to the temperature at the surface of the evaporator for controlling the sequence of operations of said electrically controlled valve and the air circulating means whereby said electrically controlled valve is closed when the temperature at the surface of the evaporator rises above freezing and the air circulating means is reactivated when the temperature at the surfaces of the evaporator.

falls below freezing after refrigerant has once more been circulated therethrough.

4. In a refrigeration machine having an evaporator through which refrigerant is adapted normally to flow for reducing the temperature at the surface and means for circulating air in surface contact with the evaporator and into the space to be cooled, a source of heated fluid, a passage communicating the source of heated fluid to an intermediate portion of the evaporator, an electrically operated valve controlling the flow of fluid through said passage, means set to operate periodically for initiating the defrost cycle whereby the electrically operated valve is caused to open to permit flow of heated fluid from the source to the evaporator and a thermostat responsive to the temperature at the surface of the evaporator for operating the electrically operated valve to shut off the flow of fluids and permit flow of refrigerant through the evaporator when the temperature at the surface of the evaporator rises above freezing and for reactivating the air circulating means when the temperature at the surface of the evaporator is reduced by the refrigerant to a temperature below freezing.

5. In a refrigeration machine having an evaporator through which refrigerant is adapted normally to flow for reducing the temperature thereof and having a pressure sensitive valve for stopping the flow of refrigerant to the evaporator when the pressure existing in the evaporator is high and permitting flow when the pressure is low, a source of high pressure heated gas, a passage communicating the source with the evaporator, an electrically operated valve controlling the flow of fluid through said passage, means set to operate periodically for initiating the defrost cycle whereby the electrical valve is operated to communicate the source of heated fluids with the evaporator to introduce high pressure heated gas into the evaporator whereby the pressure sensitive valve closes and substantially simultaneously to inactivate the air circulating means, a thermostat responsive to the temperature existing at the surface of the evaporator for initiating operation of the electrical valve when the temperature at the surface of the evaporator rises above 37 F. thereby to cut off the flow of high pressure heated gases thereto and to reestablish circulation of refrigerant through the evaporator and to reactivate the air circulating means when the temperature at the surface of the evaporator following circulation of refrigerant therethrough falls below 27 F.

6. In a refrigeration machine, an evaporator having an inlet and an outlet, a pressure responsive valve controlling the flow of refrigerant to said inlet and a fan for directing a stream of air over the surface of the evaporator, means for defrosting the evaporator comprising a source of high pressure heated gas, a passage communicating the source with an intermediate portion of the evaporator, a solenoid operated valve controlling the flow of fluid through said passage, means set for periodically initiating the defrost cycle whereby the solenoid valve is operated to establish communication between the source of high pressure heated fluid and the evaporator and substantially simultaneously to deenergize the fan, a thermostat responsive to the temperature at the surface of the evaporator for deenergizing the solenoid valve to stop flow of gases from the source to the evaporator when the temperature at the surface of the evaporator rises above 37 F. and to energize the fan for circulating air over the evaporator when the temperature at the surface of the evaporator falls below 27 F.

7. In a refrigeration system, a cooling element through which refrigerant is circulated and upon which a layer of frost accumulates during normal operation, a compressor having a low pressure side into which the refrigerant flows from the evaporator and a high pressure side from which hot ga es are emitted under high pressure, pressure responsive valve means for controlling the flow of refrigerant into the evaporator, a fan for circulating air over the evaporator and into the space to be refrigerated, a defrost system comprising a passage communicating the high pressure side of the compressor with the evaporator to introduce hot gases therein at high pressure, electrically operated valve means for controlling the flow of gases through said passage, a time switch operative momentarily to energize said electrically operated control means whereby hot gases at high pressure flow through said passage and into the evaporator thereby also to close the responsive valve and also to inactivate the air circulating means, a thermostat having a bulb located in temperature responsive relation with the surface of the evaporator, a double switch one of which is responsive to trip the thermostat when the bulb registers a temperature above freezing to deenergize the electrically controlled valve means whereby the flow of high pressure heated gas is stopped and the pressure sensitive valve automatically opens to permit circulation of refrigerant through the evaporator, the other switch being responsive to tripping the thermostat when the bulb subsequently records a temperature below freezing thereby to establish contact and to establish the air circulating means.

MYER, STEPHEN SUTTON.

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